Use the lock object : Lock : Thread C# Examples

    
using  System;
using  System.Threading;

class  MainClass
{
    private  int  Runs  =  0;

    public    void  CountUp()  
    {
        while  (Runs  <  10)
        {
            lock(this)
            {
                int  Temp  =  Runs;
                Temp++;
                Console.WriteLine(Thread.CurrentThread.Name  +  "  "  +  Temp);
                Thread.Sleep(1000);
                Runs  =  Temp;
            }
        }  
    }
    public  void  RunThreads()
    {
        Thread  t2  =  new  Thread(new  ThreadStart(CountUp));
        t2.Name  =  "t2";
        Thread  t3  =  new  Thread(new  ThreadStart(CountUp));
        t3.Name  =  "t3";
        t2.Start();
        t3.Start();
    }

    public  static  void  Main()  
    {
        MainClass  ex  =  new  MainClass();
        ex.RunThreads();
    }
}